learners support publications 1 database management system architecture

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DATABASEMANAGEMENT SYSTEM

ARCHITECTURE


• The logical DBMS architecture

• The physical DBMS architecture

DBMS ARCHITECTURE




DBMS ARCHITECTURE

The logical architecture deals with the way data is stored and presented to users.




DBMS ARCHITECTURE

The physical architecture is concerned with the s/w components that make up a DBMS.


• External or View Level

• Conceptual Level

• Internal or Physical Level

Three Level Architecture of DBMS

A major purpose of a database system is to provide users with an abstract view of the data. That is, the system hides certain details of how the data is stored and maintained.


Three Level Architecture of DBMScontinue…

View 1 View 2 View 3

Conceptual Level

PhysicalLevel

ExternalLevel


Three Level Architecture of DBMScontinue…

View 1Item_NamePrice

Conceptual Item_Number Character (6)Item_Name Character(30)Price Numeric(5,2)Stock Numeric(4)

PhysicalStored_Item Length=50Item # Type = Byte(6), offset = 0, Index = IxName Type = Byte(30), offset = 6Price Type = Byte(8), offset = 36Stock Type = Byte(4), offset = 44

ExternalLevel

Conceptual Level

PhysicalLevel

View 2Item_NameStock

Sales Officer Inventory Controller


This level is closest to the users and is concerned with the

way in which the data is viewed by individual users.

Most of the users are not concerned with all the

information contained in the database. Instead they

need only a part of the database relevant to them. The

system provides many views for the same database.

External or View Level


• Highest level of abstraction of database.

• Allows to see only the data of interest to them.

• Users – Application programmers or end-users.

• Any no. of external views – external schema.

External or View Levelcontinue…


• It consists of the definition of logical records and

relationships in the external view.

• It also contains the methods for deriving the

objects such as entities, attributes and relationships

in the external view from the Conceptual View.

External or View Levelcontinue…


This level of abstraction describes what data are actually stored in

the database. It also describes the relationships existing among

data. At this level, the database is described logically in terms of

simple data-structures. The users of this level are not concerned

with how these logical data structures will be implemented at

the physical level, rather they just are concerned about what

information is to be kept in the database.

Conceptual Level


• The sum total of DBMS users view.

• Describes what data are actually stored in the

database (ie,all the records and relationships

included in the database).

Conceptual Levelcontinue…


• The conceptual view is a representation of the

entire information content of the database in a

form that is some what abstract in comparison

with the way in which the data is physically

stored.



• The conceptual view is defined by means of the

conceptual schema, which includes the

definition of each of the various types of

conceptual records and the mapping between

the conceptual schema and the internal schema.



• Lowest level of abstraction.

• Describes how the data are physically stored.

• Internal view – internal schema (not only defines the

various types of stored record but also specifies what

indexes exists, how files are represented, etc.)

Internal or Physical Level


The internal level is closest to physical storage.

This level is also termed as physical level. It

describes how the data are actually stored on

the storage medium. At this level, complex low-

level data structures are described in detail.

Internal or Physical Level


The ability to modify a schema definition in one level

without affecting a scheme definition in the next higher

level is called DATA INDEPENDENCE

• Physical Data Independence

• Logical Data Independence

Data Independence


It refers to the ability to modify the scheme followed at the

physical level without affecting the scheme followed at the

conceptual level.

The application programs remain the same even though the scheme

at the physical level gets modified.

Modifications at the physical level are occasionally necessary in

order to improve performance of the system.

Physical Data Independence


It refers to the ability to modify the conceptual scheme without

causing any changes in the schemes followed at view levels.

The logical data independence ensures that the application

programs remain the same.

Modifications at the conceptual level are necessary whenever

logical structures of the database get altered because of some

unavoidable reasons.

Logical Data Independence


It is more difficult to achieve logical data independence

than the physical data independence.

The reason being that the application programs are

heavily dependent on the logical structure of the database.

Physical & LogicalData Independence


• Describes the software components used to

enter and process data.

• How these s/w components are related and

interconnected.

Physical DBMS Architecture


DBMS Structure

Object CodeOf Program

DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms

General users AP Query DBA

Data Files Data Dict.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



DDL – set of commands required to define the format of data.DML – set of commands that modify, process data.DML precompiler converts DML statements embedded in an application program to normal procedural calls in the host language. It interacts with the query processor in order to generate the appropriate code.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



DDL compiler converts DDL statements into a set of tables containing metadata tables – which are in a form that can be used by other components of the DBMS. These are stored in system catalog or data dictionary.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Manages the allocation of space on disk storage.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Responsible for receiving query language statements and changing to a form the DBMS can understand. It has two parts : (i) parser (ii) query optimizer


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



It is the interface b/w low-level data, application programs and queries. It enforces constraints to maintain the consistency and integrity of the data as well as its security. It synchronizes the concurrent access. It also perform backup and recovery operations.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components

• Authorization Control• Command Processor• Integrity Checker• Query Optimizer• Transaction Manager• Scheduler• Recovery Manager• Buffer Manager


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


Checks that the user has necessary authorization to carry out the required function.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


Converts commands to a logical sequence of steps.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


Checks the requested operation satisfies all necessary integrity constraints such as key constraints.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


Examines the query language statements and tries to choose the best and most efficient way to executing the query. Factors – CPU time, disk time, network time, sorting methods and scanning methods.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


The transaction manager maintains tables of authorization concurrency.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


It controls the relative order in which transaction operations are executed.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


Ensures that the database remains in a consistent state in the presence of failures. Responsible for transaction commit and abort.


DBMS Structure


DMLPrecompiler

QueryProcessor

DDLCompiler

DatabaseManager

FileManager

DatabaseSchema

SystemCalls

ApplicationPrograms



Components


Responsible for the transfer of data between main memory and secondary storage.


Questions ?

learners support publications 1 database management system architecture

Documents

level architecture of

view level slide

conceptual level slide

physical architecture

learners support publications

logical dbms architecture

conceptual view

highest level of abstraction